The present invention relates to thermoplastic compositions, and especially to compositions containing a crystallizable thermoplastic which is itself isotropic (non-liquid crystalline) with an oligomeric thermotropic (liquid crystalline in the melt) additive.
Various additives have been proposed to crystallizable isotropic thermoplastics such as polyamides (e.g. nylon 6) and polyesters (e.g. poly(ethylene terephthalate)) which are intended to improve the physical properties of fibers or films found therefrom. Such additives include inorganic materials, small organic compounds and large polymers with which the isotropic thermoplastic is coextruded or otherwise blended. With the discovery of thermotropic polyesters, as described, for example, in U.S. Pat. Nos. 4,140,846 to Jackson, Jr. et al. (Feb. 20, 1979), 3,890,256 to McFarlane et al. (June 17, 1975), 3,991,013 to Pletcher (Nov. 9, 1976), 4,066,620 to Kleinschuster et al. (Jan. 3, 1978), 4,075,262 to Schaefgen (Feb. 21, 1978), 4,118,372 to Schaefgen (Oct. 3, 1978) and 4,156,070 to Jackson, Jr. et al. (May 22, 1979), some proposals have been made to blend these materials with isotropic polymers. Unfortunately, thermotropic polymers have thus far proved incompatible with isotropic polymers, with the heterogeneous blends that are formed exhibiting properties no better than the isotropic polymers alone.
In particular, M. Takayanagi et al. in J. Macromol. Sci, - Phys., B17(4), pp. 591-615 (1980) report attempts to blend nylon-6 or nylon-66 with wholly aromatic polyamides such as poly-p-benzamide or their block copolymers with nylon-6 or nylon-66. The wholly aromatic polyamides used are infusible.
M. Wellman et al., Division of Coating and Plastics Preprints, American Chem. Soc., vol 43, pp 783-87 (1980) report blending of rod-like polymers with similar coil-like polymers, both having monomers with fused ring structures (e.g. poly-para-phenylene benzobisthiazole and poly-2,5(6) benzimidazole). Again the rigid polymer is infusible.